Mr Thomson on the Parallel lioads of Lochaber. 51 



the possibility of doubt, that the Parallel lioads are the 

 beaches of ancient lakes, which have been maintained amonfj 

 the mountains by barriers across the lower parts of the glens. 



With reference to objections to the supposed existence of 

 barriers which had previously been brought forward, Mr 

 Milne remarks — " These objections resolve entirely into the 

 difficulty of explaining the disappearance of the barriers, 

 which must have dammed back the water in the valleys : 

 but it would be no good reason for rejecting an explanation 

 founded on the existence of bai'riers, even though we could 

 not very clearly account for the disappearance of them, pro- 

 vided that there is direct and conclusive evidence that such 

 barriers existed. Now, I conceive that there is such evi- 

 dence fui'nished by the considerations before referred to.'' 

 Ideas similar to these of Mr Milne had also occurred to Sir 

 Thomas Dick Lauder nearly thirty years ago, and, in a paper 

 which he laid before the Royal Society of Edinburgh, they 

 are expressed in the following terms : — " I believe it will 

 be readily admitted, that it is much easier to suppose the 

 existence of former banners, than to discover the means 

 which operated in their removal ; but it must be also 

 granted, that the difficulty of accounting for the destruction 

 of such large masses, does not by any means imply that they 

 never had any being at all, particularly where a number of 

 facts remain to lead us to an opposite conclusion. From all 

 the present appearances it is extremely probable that the 

 barrier of Loch Roy was not only very thin, but of soft ma- 

 terials, at the two parts which have been removed." 



Thus, both Sir Thomas Dick Lauder and Mr Milne have 

 come decidedly, and, I think, with good reason, to the conclu- 

 sion that barriei's did exist ; but tlien we are by no means ob- 

 liged to assume, that these were composed of earthy materials. 

 It is in this assumption, in fact, that all the difficulties con- 

 nected with the*explanations given by these two writers arc 

 involved ; and to me it seems perfectly clear that the bar- 

 riers in reality were formed of glaciers. 



The glacial explanation of the Parallel Roads given by 

 Agassiz in his paper in Jameson's Journal for 1842, was 

 neeossarily imperfect in its details. Sufficient facts in regard 



